A radioactive exit sign is safe and effective because the type of radiation that’s used is non-toxic to the human body. The tritium units contain such a low amount of the radiation that it can be flushed from the human body should ingestion occur. The lights are very effective because they function in the most extreme conditions without the need for a backup battery.
All exit signs are required to function in extreme conditions. Some fixtures are attached to an electrical feed that keeps the light on when there’s a power source. When there is no power source, these types of exit lights also have a back up battery that will keep the light on for 90 minutes. Often, an additional 24 hours of electrical charging is required for the unit’s back up battery to function again after it’s used up the first 90 minutes of battery power.
Radioactive exit signs contain tritium, a radioactive isotope of hydrogen. It’s an isotope of the hydrogen element and has the chemical symbol H-3. There are a few places that tritium can be found naturally in the environment. A common place is the upper atmosphere where the cosmic rays striking air molecules produce this radioactive product.
The concentrations of tritium produced naturally are generally very low. When produced closer to the Earth’s service, the radioactive isotope of hydrogen is found in the form of tritiated water. It can be easily disbursed in water bodies, soil, and the atmosphere. For this reason, people are often exposed to small amounts of this chemical since it’s commonly found in the food chain and the environment.
Radioactive exit signs are safe and effective because they use a radioactive chemical that is already found naturally in the environment and to which the average person has already been exposed to. Tritium can also be found in other items that require self-illumination. Examples of such devices include glow in the dark paints, aircraft dials, wristwatches, gauges and of course exit signs on buildings. The isotope is considered to be much safer than radium, a chemical that was once used as a luminescent source for gauges and watches. Radium is now considered to be a hazardous substance and has been banned for use in the United States.
The radioactive exit sign uses tritium, which was discovered in 1934 by Ernest Rutherford and his team. The scientists bombarded a Deuterium atom with nuclei of Deuterium atoms in a method that simulated the way nitrogen molecules are bombarded by cosmic rays in the upper atmosphere.
Tritium in the atmosphere gets decayed by beta emission and has a lifespan on 12.5 years, but when used in exit lights, can produce light for as long as 25 years.